Because throwing a trillion dollars worth of resources down a black hole is stupid in a world with limited resources and billions of poor people.
Also worth noting: despite the writings of Pascal, you won't find many atheists in church. Most of them decide the cost is not worth the (odds-adjusted) expected benefits.
What keeps me out of church is the fact that the Bible could just as easily have been written by Satan, and that following Jesus would condemn me to hell.
Now, granted, global warming is more likely, to me, than hell, but not nearly as hot, so it's a lot more worth considering the costs involved :)
Funny, I always thought the best ways to fight climate change, if it exists, were to use less and make what is left more efficient. That is why I don't see it as a bad thing- in a world with limited resources and billions of poor people, increased efficiency and decreased consumption seems like a good thing.
OK, sure. So, let's say we develop technology that allows us to lower our emissions by a whopping 80% compared to today. OK, now imagine that India, rural China, the middle east, South America, and Africa develop into first world nations. The world CO2 emissions would end up back where they are today, despite the revolutionary technologies developed and employed.
By which I mean to say that forcefully curbing CO2 emissions is a very, very hard problem. And curbing CO2 emissions without forcing developing nations not to develop is even more difficult.
Personally I think that even if global warming is every bit its cracked up to be the Bangledeshis, for example, will probably be better off with higher sea levels and first world wealth and infrastructure than they would be with existing sea levels and another century of poverty.
I'm not a climatologist, but rising sea levels are not the only problem. They are simply the most commonly selected problem to cite, as 'submerged cities' strikes close to home, and is a classical apocalyptic (and thus greatly feared) event.
There are far more consequences than just that. For example, all the coral of the entire ocean would be dead or dying. Not that I expect you to care about coral; that is just one example.
It's like Pascal's Wager, imho.